Electric ignition system



July 3, 1956 w. B. SMITS 2,753,389

ELECTRIC IGNITION SYSTEM Filed Feb. 12, 1952 //Vl E/V7 0/? 144 725 5055/1/73 By Qua United States Patent ELECTRIC IGNITION SYSTEM Wytze BeyeSmits, Voorburg, Netherlands, assignor to Smitsvonk N. V., Rijswijk (S.H.), Netherlands Application February 12, 1952, Serial No. 271,117

2 Claims. (Cl. 123-148) The invention relates to an electric ignitionsystem with a surface discharge spark plug, a condenser, a magneto forcharging this condenser, and a switch by means of which the spark plugcan be periodically connected in parallel with the condenser.

The invention aims at providing an electric ignition system which isextremely simple in construction and particularly suitable for theinternal combustion engine of a bicycle with a light motor. It ischaracterized in that the magneto consists of a rotatable permanentmagnet and a stationary armature provided with a winding, a cam foroperating the switch is provided on the rotatable member with thepermanent magnet, the condenser is connected on the one hand to thecontact of said switchwhich contact can be moved by means of saidcam-and on the other hand to the ground, the spark plug is connected onthe one hand to a fixed contact of the switch and on the other hand tothe ground, and the condenser is connected in parallel with the armaturewinding of the magneto at least during the period that the connectionwith the spark plug is broken.

In this system the armature of the magneto need only be provided with asingle coil, to which the ignition condenser is connected at leastduring the large part of the revolution of the permanent magnet. Theswitch provides for the condenser being connected to the spark plug atthe moment when the former holds a charge. The cam for operating theswitch should therefore be adjusted and designed in such a way that theswitch is operated at the moment when the voltage generated in thearmature coil exceeds a given value, for example when it has attainedalmost its maximum value. The said cam is preferably so designed andoperates the moving contact of the switch in such a manner that thiscontact is passed from the position of rest to the position in which thespark plug is connected to the condenser by a rotation of the permanentmagnet through at most The condenser may be permanently connected to thearmature coil. In that case the switch may be an ordinary switch, whilethe armature coil, with the condenser connected via it, is connected onthe one hand to the ground and on the other hand to the moving switchcontact.

In many cases it is to be preferred to disconnect the condenser from thearmature winding before it is connected to the spark plug. A purecondenser discharge is thus obtained. The switch should then be achangeover switch, with the moving contact connected to the condenserand the fixed contacts to the armature Winding and the spark plugrespectively.

It is advantageous for the permanent magnet to be provided on theflywheel of the internal combustion engine, and for this flywheel toenclose a space in which at least the armature, the switch and the camfor operating the switch are accommodated. The condenser may also belocated in the space enclosed by the flywheel.

In the system according to the invention not only is the current impulserequired for the ignition generated direct by the flywheel, but theflywheel also serves to produce the ignition spark at the right moment.Some readjustment of the moment at which the spark is produced ispossible when the fixed contacts of the switch are adjustable in thedirection of rotation of the moving switch contact.

The invention is explaned with reference to the drawing, whichillustrates two embodiments of the invention in a very diagrammatic way.In this drawing Fig. 1 is a diagram of an electric ignition system whichis accommodated in the flywheel of an internal combustion engine andoperates by means of a switch,

Fig. 2 is a diagram of a variant of the system according to Fig. 1, and

Fig. 3 shows a voltage curve.

In Fig. l, the numeral 1 designates the flywheel of an internalcombustion engine, for example a light motor of a bicycle. 2 and 3 arethe poles of a permanent magnet provided in the rim of this flywheel 1.The numeral 4 designates a stationary armature, which cooperates withthe permanent magnet 2, 3 and is provided with a single coil 5. In thespace enclosed by the rim of the flywheel, a change-over switchconsisting of a reciprocating switch arm 6 and two adjustable fixedswitch contacts 7, 8 has been accommodated. The fixed contact 7 isconnected to the armature coil 5, the other end of which is connected toa spark plug 9, which is likewise connected to the ground. The movingswitch arm 6 is connected to the ground. On the shaft 11 of the flywheela cam 12 for operating the switch arm 6 has been provided.

Whenever the flywheel 1 moves with the poles 2, 3 of the permanentmagnet past the ends of the armature 4, an alternating voltage isgenerated in the coil 5. The cam 12 is provided on the shaft 11 in sucha way and has such a shape that the switch arm 6 of the contact 7 isforced from and against the contact 8 when the voltage generated in thecoil 5 has a given value, for example when it is practically equal tothe maximum amplitude of this voltage. The condenser 10 is thereforefirst charged, then disconnected from the coil 5, and subsequentlyconnected to the spark plug 9, so that it can discharge via this sparkplug. The cam 12 has such a shape that the change-over takes placewithin an angle of rotation of 10 of the flywheel.

In Fig. 2 the condenser remains connected in parallel with the armaturecoil 4. The advantage of this is that the switch need not be achange-over switch, and the switching need not take place with the samehigh degree of accuracy as in the case according to Fig. 1. Further itwill not be possible for the voltage peak in the armature coil to attainan inadmissible value when the flywheel rotates very rapidly, as in thefirst case, because the condenser remains connected to the armaturecoil. A safety spark gap, which will frequently have to be provided inthe case according to Fig. 1, is now superfluous. A drawback of theswitching device according to Fig. 2 is that all the energy generated inthe armature coil is conducted through the spark plug, and thatconsequently the consumption of the electrode material of the spark plugis greater than in the case according to Fig. 1. This switching devicetherefore does not produce a pure condenser discharge on the spark plug.

Fig. 3 shows the curve of the voltage on the condenser in the switchingdevice according to Fig. 2.

I claim:

1. An ignition system for an internal combustion engine in which lowvoltage surface discharge spark plugs are utilized, in combination, acondenser, rotatable means including a camshaft for alternatelyconnecting said condenser with a source and a low voltage spark plug,said source comprising a stationary armature and a rotatable permanentmagnet, said rotatable permanent magnet being mounted in the rim of aflywheel disposed on said camshaft. V

2. An ignition system for an internal combustion engine comprising incombination a low-voltage surface discharge spark plug, a condenser, asource for charging said condenser, switch means for alternatelyconnecting said condenser with said source and said low-voltage sparkplug, a camshaft, rotatable cam means for actuating said switch mountedon said camshaft, said source comprising a stationary armature and arotatable permanent magnet, said rotatable permanent magnet beingmounted in the rim of a flywheel mounted on said camshaft.

References Cited in the file of this patent UNITED STATES PATENTSReichenbach Dec. 27, 1904 Apple June 6, 1905 Kent Nov. 13, 1917 PlummJune 19, 1923 Smits July 26, 1938 Scott May 3, 1949 Raliegh Jan. 9, 1951

